<ImageButton>:
    size_hint: None, None
    size: self.texture_size
    pos_hint:{'center_y':.5}

    canvas.before:
        PushMatrix
        Scale:
            origin: self.center
            x: .75 if self.state == 'down' else 1
            y: .75 if self.state == 'down' else 1

    canvas.after:
        PopMatrix